A compact is a polycrystalline mass of abrasive particles (e.g. diamond and cubic boron nitride) bonded together to form an integral, tough, coherent, high-strength mass. A composite compact is a compact bonded to a substrate material, such as cemented, metal carbide (e.g. cobalt cemented tungsten carbide). The metal bonded carbide mass is generally selected from the group consisting of tungsten carbide, titanium carbide, tantalum carbide and mixtures thereof with metal bonding material therein normally being present in a quantity from about 6 to 25 weight percent and selected from the group consisting of cobalt, nickel, iron and mixtures thereof.
Compacts or composite compacts may be used as blanks for cutting tools, drill bits, dressing tools, and wear parts. Compacts made in a cylindrical configuration have been used to make wire drawing dies (see U.S. Pat. Nos. 3,831,428; 4,129,052; and 4,144,739).
One method for manufacturing compacts involves the steps of:
A. placing within a protective shield metal enclosure which is disposed within the reaction cell of a high pressure/high temperature apparatus;
(1) a mass of abrasive crystals (either diamond or cubic boron nitride (CBN); and PA0 (2) a mass of catalyst metal in contact with the mass of abrasive crystals; and
B. subjecting the contents of the cell to conditions of temperature, pressure and time sufficient to give intercrystal bonding between adjacent crystal grains.
For example, the mass of catalyst metal could be in the form of a disc of one of the well known catalysts for diamond or CBN crystallization. Under the HP/HT conditions, a compaction front advances through the dense diamond or CBN material, and the catalyst metal (in liquid form) makes itself available as a catalyst or solvent for recrystallization or intercrystalline bonding of the diamond or CBN grains. This process is sometimes known as the sweep through method, i.e., the catalyst sweeps through the diamond or CBN mass.
The relative shapes of the abrasive mass and catalyst can be varied. For example, the mass of diamond or CBN can be cylindrical, and the catalyst can be an annular shape surrounding the cylinder of abrasive crystals.
The source of catalyst may also be cemented metal carbide or carbide molding powder wherein the cementing agent is a catalyst or solvent for diamond or CBN recrystallization of growth.
The catalyst is generally selected from cobalt, nickel and iron or aluminum alloy in the case of CBN. The catalyst may be mixed with the abrasive crystals in addition to or instead of being a separate mass adjacent to the abrasive crystals.
Also, in place of abrasive grains such as diamond or CBN, one may choose to utilize as raw materials other sources of carbon or boron nitride such as graphite, hexagonal boron nitride or wurtzite boron nitride which would be converted to diamond or CBN respectively during the HP/HT process. Processes for such conversions are described in the patent literature, for example, U.S. Pat. Nos. 3,407,445 and 3,850,053 (for diamond) and British Pat. No. 1,317,716, U.S. Pat. Nos. 3,212,852 and 4,118,194 and U.S. Pat. No. 4,289,503 (for CBN), all of which are hereby incorporated by reference.
High temperature and high pressure in the diamond or CBN stable region are then applied for a time sufficient to bond the abrasive crystals together. The resulting compact is characterized particularly by diamond-to-diamond or CBN-to-CBN bonding, i.e., intercrystal bonding between adjacent grains whereby there are parts of the crystal lattice which are shaped between neighboring crystals (resulting from recrystallization at HP/HT conditions). Methods for making diamond compacts are detailed in U.S. Pat. Nos. 3,141,746; 3,745,623; 3,609,818; and 3,850,591; and processes for CBN compacts are disclosed in U.S. Pat. Nos. 3,233,988; 3,743,489; 3,767,371; and 4,188,194 (all of which are incorporated herein by reference).
The manufacture of thermally stable compacts is described in U.S. Pat. No. 4,224,380. This patent teaches the removal of substantially all of the metallic (catalyst) phase from compacts to yield a compact consisting essentially of self-bonded abrasive particles with an interconnected network of pores disposed throughout. Such compacts can withstand exposure to temperatures of about 1200.degree. C. to 1300.degree. C. without substantial thermal degradation, an advantage over the compacts of, for example, U.S. Pat. No. 3,745,623 which are thermally degraded at a temperature between 700.degree. C. and 800.degree. C. The metallic phase is removed by acid treatment, liquid zinc extraction, electrolytic depletion, or similar processes. The compacts of this type will be referred to throughout as thermally stable compacts.
The current manufacturing methods of thermally stable compacts require a post pressing step, such as laser cutting, grinding, or lapping, for shaping each piece to the desired configuration, (e.g. triangular or segment of a circle). This consumes time, labor and materials. Since diamond is the hardest known material and CBN the second hardest, the polycrystalline mass is most difficult to shape. The shaping step, whether by laser cutting, dicing with a diamond wheel, or other method, requires labor intensive handling for each final piece. This adds to the cost, logistics and time required to manufacture the product. The crushing or milling of large polycrystalline pieces is not a viable method because the shape cannot be controlled and only a small percentage of the desired particle size is obtained. The problem is, therefore, to eliminate the individual handling requirements for each piece while maintaining the desired shape of the pieces.
U.S. Pat. No. 3,949,062 describes one method for producing diamond compacts of a predetermined shape by surrounding a monolithic piece of graphite or a predetermined shape with catalyst and transforming it into polycrystalline diamond through a high pressure/high temperature process using a pulse of electric current.
U.S. Pat. No. 3,785,093 proposes making sintered diamond and cermet mixtures by exposing such mixtures to conditions within the graphite (non-diamond) stable region while contained within graphite shells which are in turn contained within shells made of low melting metals (e.g. zinc).
The diamond stable region is the range of pressure temperature conditions under which diamond is thermodynamically stable. On a pressure-temperature phase diagram, it is the high pressure side, above the equilibrium line between diamond and graphite. The cubic boron nitride stable region is the range of pressure temperature conditions under which cubic boron nitride is thermodynamically stable. On a pressure-temperature phase diagram, it is the high pressure side, above the equilibrium line between cubic boron nitride and hexagonal boron nitride.
In the case of normal (i.e. non-thermally stable) diamond or CBN compacts, there is another problem connected with their use, not the manufacturing finishing steps. Diamond and CBN compacts, such as those manufactured by the catalyst sweep through method, and very strong but very brittle materials. Once started, fractures can propagate through the diamond or CBN mass. The chips formed can be quite large and can limit the usefulness of the material. This is particularly true in the case of petroleum or rock drill bits where massive failure of the diamond layer of a composite compact can also lead to damage of the remaining cutters on the bit. A technique is needed which would reduce the massive failure caused by fractures propagating through a well bonded polycrystalline brittle material such as the diamond layer of compact cutters used in petroleum drill bits.
U.S. Pat. No. 4,255,165 describes a modification of composite compacts in which at least two connected metal carbide masses are bonded to and interleaved with at least two masses of polycrystalline diamond or CBN. This modification is said to provide internal reinforcement of the composite compact against massive fracture by enhancing resistance to crack propagation.
U.S. Pat. Nos. 4,063,909 and 4,108,614, as well as South African Patent Application No. 77/5521 disclose interposing a transition metal layer between the diamond particles and metal carbide of various types of composite compacts during manufacture.
British Pat. No. 1,568,202 discloses laminated compacts in which bonding between adjacent diamond layers takes place through a metal or alloy layer.